Aqueous cooling solution and method of inhibiting corrosion in cooling system



United States Patent 3,147,223 AQUEOUS COOLING SOLUTION AND METHOD OF INITING CORROSION 1N COOLING SYSTEM David B. Boies, Chicago, and JohnL. Gerlach, Bridgeview, 1.1L, Louis C. Larsonneur, Tyler, Tex., and Jacob I. Bregman, Park Forest, 111., assignors to Nalco Chemical Company, Chicago, Ill., a corporation of Delaware No Drawing. Filed Oct. 14, 1959, Ser. No. 846,271 5 Claims. (Cl. 252-75) The present invention relates to corrosion inhibitors, to noncorrosive liquids, and to methods for inhibiting corrosion. More particularly, the invention relates to compositions and methods for the prevention of corrosion in heat exchange devices employing aqueous solutions, especially in the cooling systems of internal combustion engines such as automotive and diesel engines.

Many organic and inorganic chemicals have been added to aqueous cooling systems to prevent corrosion. Buttered chromates, for example, are widely used by railroad companies for this purpose. Although such compounds are among the most effective of the known corrosion inhibitors, they are not entirely satisfactory, partly because many persons are dermatitis sensitive to chromates. Other processes and compounds that have been tried in anticorrosion systems either offer less protection than is needed or have other disadvantages. Certain of the inhibitors cause a deposit formation which reduces cooling efliciency, while others attack nonmetallic parts of the cooling system or are not sufficiently water-soluble or water dispersible. Several of the known inhibitors are too costly to use on a commercial scale. Many others lose theiretfectiveness where antifreeze solutions are employed.

It is, therefore, an object of the present invention to provide a corrosion inhibitor which may be employed advantageously with cooling waters and which is especially desirable for diesel engine cooling systems and for waterorganic antifreeze solutions. a

It is another object of the invention to provide an oilrr type corrosion inhibitor which provides improved protection for various metals and other materials found in the cooling systems of internal combustion engines.

Another object is to provide corrosion inhibitors which are superior to chromates and which do not cause excessive skin or eye irritation.

Still another object of the invention is to provide a method and composition which is effective over a wide concentration range and which is not affected by variations in the hardness or dissolved solids content of the cooling fluid.

Other objects will become apparent to those skilled in the art from the following detailed'description of the invention.

In general, it has been found that the above described objects as Well as others are achieved by using as a corrosion inhibitor a composition consisting of an oil-soluble petroleum sulfonate, mercaptobenzothiazole, a low aromatic mineral oil, and certain dispersing or solubilizing agents. More particularly, it has been found that if a petroleum sulfonate having a molecular weight of from about 415 to about 525 or more (preferably 500-525) is combined with mercaptobenzothiazole and a mineral oil within certain concentration ranges and with suflicient 3,147,223 Patented Sept. 1, 1954 amounts of dispersing or solubilizing agents, a composition is formed which disperses well in water and in aqueous antifreeze solutions, and which provides excellent corrosion protection for all types of metals.

Oil-soluble petroleum sulfonates are soaps of oil-soluble petroleum sulfonic acids commonly known as mahogany acids. They are produced by a controlled reaction between sulfuric acid and petroleum distillates. The oilsouble or olephilic sulfonic acids in the upper oil layer are converted to salts by neutralization, preferably with an alkali metal or ammonium hydroxide. The sulfonates are removed from the oil by suitable extraction media, then they are concentrated and further purified. In general, petroleum sulfonates which have molecular weights above 400 are classified as oil-soluble, while those with molecular weights below 400 are water-soluble or hydrophilic petroleum sulfonates. The oil-soluble sulfonates may be dispersible in water but are not water-soluble. Methods for the production of the oil-soluble petroleum sulfonates are well known and are described in the literature. US. Patent 2,412,633, for example, contains a description of their production, as well as various soaps or salts of the petroleum sulfonic acids which are contemplated, including the alkali and alkaline earth metal salts and ammonium or amine salts.

The corrosion inhibitor should contain from about 2.5 to about 25% active sulfonate. As was suggested above, sulfonates having molecular weights of from about 415 to about 525 are satisfactory. It is preferred that the molecular weight be on the high side of this range, that is, from about 500 to 525.

It is important that there be at least about 10 p.p.m. of mercaptobenzothiazole in the inhibited water when the formulation is at use concentration. When 0.5% of inhibitor is added to the cooling system, the inhibitor should contain from 0.1 to 2.0% of mercaptobenzothiazole, and preferably from 0.4 to 0.8% of mercaptobenzothiazole.

In general, any dispersing or solubilizing agent which satisfactorily permits the emulsification of oil-in-water may be used. Such agents include n-butyl alcohol and Triton X-114, which is an ethoxylated nonyl phenol. Other dispersing agents which are particularly effective are poly-propylene glycol, Sterox A] which is an aliphatic nonionic polyoxyethylene ether; various surfactants such as G-1425 or G-1441 which are polyoxyethylene sorbitol lanolin derivatives, and Tween 81 which is a polyoxyethylene sorbitan mono-oleate. Solubilizing agents which can be used in the subject invention include isopropanol and ethylene glycol. The n-butyl alcohol concentration can range from 0 to about 15% as needed. It has been found that from 2 to 5% Triton X-114 provides satisfactory results.

The balance of the composition consists of the oil. The ratio of active sulfonate to oil can vary from approximately 2.5:97.5 to 35:65. It is essential that the oil not be aggressive toward rubber and other nonmetallic parts of the cooling system. Low aromatic petroleum distillates containing mixtures of aliphatic and naphthenic hydrocarbons varying from C to C satisfy these requirements. Hydrocarbons having longer or shorter chain lengths could also be used, but in some instances the shorter molecules would have too low a flash point, and in other cases the longer chained hydrocarbons would have too high a pour-point to be convenient. The aromatic content of the oil should not be higher than a few percent inasmuch as the presence of aromatic compounds increases the attack on the rubber components of a cooling system. Certain types of rubber are more sensitive to the presence of aromatic compounds than others. In general, it is preferable that the oil be no more than about 20% aromatic, although certain rubber materials are able to withstand even higher aromatic levels. The best results from the standpoint of attack on rubber components are obtained where the oil contains little or no aromatic compounds. The oil need not be a mineral oil.

Vegetable and animal oils, however, give only fair results in that they are not as anticorrosive as mineral oils, and

because they have more of a tendency to attack rubber and are more expensive than mineral oils.

The inhibitor is preferably added to the cooling liquid in amounts from about 0.1% to about 2.5%. This quantity can vary inasmuch as less than 0.1% (0.05, for example) perceptibly lowers corrosion rates, and amounts from 2.5% up to or more can be used although such quantities are not economically feasible.

The inhibitor is highly effective with aqueous antifreeze solutions containing materials such as methanol, ethylene glycol, propylene glycol, and glycerine. The composition may also be employed in cooling waters containing no organic liquid.

In the examples set forth below, several methods were employed to determine the effectiveness of the subject inhibitors. They include the so-called flask and recirculating tests.

The flask test is usually run in a wide mouth one liter Erlenmeyer flask equipped with a reflex condenser and an aeration tube. In our work, the aeration tube was made of 2 mm. glass tubing, and was surrounded by a glass chimney to prevent impingement of the air on the specimens. The specimen assembly was supported in the solution by hooks of Nichrome wire. The flask was immersed in an oil bath at the desired temperature.

The standard test water consisted of one part Chicago tap water to one part distilled water, with grains of sodium chloride added per gallon. One liter of solution was used, and the temperature was maintained at 180:5" F. Test water having other compositions were used as noted in the examples.

The specimens employed in the tests were picked for their similarity to metals used in diesel and automotive cooling systems. The specifications for each specimen were as follows:

(a) Brass: The brass specimens were strips measuring 1 inch by 1 /2 inches by inch. The composition is given by specification SAE 70 grade C.

(b) Copper: The copper specimen consisted of a strip measuring 1 inch by 1 /2 inches by inch, conforming to specification ASTM B133-47T.

(c) Solder: The solder specimen consisted of a piece of either 9 or 10 gauge solid solder, having a surface area of 1.2 square inches. One end was flattened and a mounting hole drilled. The composition of the solder was 45% tin and 55% lead. The specimen was bent in the form of a loop.

(d) Aluminum: The aluminum specimens used in these tests were made from cast strips of Alcoa 319 alloy. These specimens were milled to 1 inch x 1% inches x /1 inch.

(e) Cast iron: The cast iron specimens were supplied by a locomotive manufacturer, and were cut from a diesel cylinder liner. They were of a typical nickel cast iron, having an approximate analysis as follows:

Percent Total carbon 3.1 Combined carbon 0.5 Manganese 0.8 Silicon 1.9 Chromium 0.3

Nickel 1.3

Molybdenum 0.4

4 The specimens measured about 1 inch by 2 inches by inch. If the inner wall was chrome-plated, the plating was removed by milling.

(f) Radiator tube: The radiator tubing specimen was 1% inches in length and Was cut from diesel radiator tubing. It was made of brass Cul5% Zn) coated with tin.

The area of the specimen to the volume of liquid ratio was as follows.

Square inches Specimen: per gallon Cast Iron 23 Aluminum 15 Solder 8 Radiator tube 10 Copper 11 Brass 11 Procedure:

(a) C0upled.After preparation, the specimens were weighed and then mounted on a 632 brass screw. The specimens were separated by Ms inch conical brass washers, so that they were in electrical contact. They were placed on the screw in the following order: solder or radiator tube, cast iron, copper, brass, and aluminum. The assembly was then placed in the test solution at F., being suspended from the Nichrome hooks. After one week, the specimens were removed, cleaned, and reweighed. The extent of corrosion was determined by weight loss and/ or visual examination.

The specimens were prepared as follows:

Cast iron, aluminum, copper, brass: Sand blasted, wiped with dry cloth; then rinsed in acetone and toluene.

Solder: Rubbed well with a rag wet with toluene.

Radiator tube: Cleaned first with toluene, and then washed with soap and Water.

The specimens were cleaned after the test as follows:

Cu and brass: Washed with water, dipped in inhibited HCl for 15 seconds, and then dipped in soda ash and rinsed with water.

Solder and radiator tubing: Washed lightly with water and cleanser, and then rinsed and dried.

Cast iron: Cleaned with soap and water, dipped 30 seconds in inhibited HCl, then in soda ash solution, and finally rinsed and dried.

Aluminum: Immersed at 180 F. in 2% CrO 5% H PO solution for 10 minutes.

Cleaning losses were as follows:

Mg. Copper 0.3 Brass 0.2 Aluminum 0.2 Cast iron 0.4 Solder 0.5 Radiator tube 0.5

(b) Uncoupled flask tests.The specimens were insulated from each other by suspending them on a glass rod with rubber spacers. The solutions were aerated at 180 F. and the test period was one week. The specimens included radiator tubing, a cast iron liner, copper, brass, and aluminum. Testing conditions and procedures otherwise were identical with the coupled flask tests.

(0) Recirculating test-The recirculating test was designed to more nearly duplicate actual conditions in a diesel cooling system, and to give a final laboratory evaluation of a treatment. Water was circulated by means of a bronze centrifugal pump from a five gallon glass reservoir through a 2 /2 foot length of W inch, 20 gauge seamless steel cold drawn tubing which was heated by means of 20 Bunsen burners. The water then flowed through a cooling section consisting of two 12 inch lengths of /8 inch copper tubing, jacketed by cooling water, thermostatically controlled to give an effluent temperature of the system water of 180 F. From the cooler the water flowed through a 16 mesh copper screen, then back to the reservoir. All of the various metal parts of the system were in electrical contact. Flow through the system was approximately 0.5 gal/minute. Two sets of specimens were suspended in a reservoir containing standard test water. In one set the five metals were in contact, while in the other set the metals were electrically insulated from each other by means of rubber washers on a glass rod. After the test, the specimens were cleaned and reweighed to determine weight loss. The degree of corrosion and scale formation was determined by cutting open the heat transfer tube at the end of the test, and also by inspecting the screen for deposit.

EXAMPLE I The effectiveness of the subject corrosion inhibitor was compared with the elfectiveness of buffered chromate and with a system without a corrosion inhibitor in the above described flask and recirculating tests at a dosage of 0.5%. The results of the test were as follows:

Corrosion Rates (m. p.y.)F lask Test Bufiered Subject Chromate Blank, Treatment Ingibtfr (2,100 No Treat- .5 p.p.m. men

NazCrO4) 1 Coupled Test:

Cast iron 0. 0 0. 2 18.6 0.2 0. 7 0. 3 0. 0 0. 5 0. 3 0. 0 18. 7 18. 3 0. 2 0.2 0. 6

Cast lron 0.0 0. 3 10. 2 Copper 0. 5 0.8 0. 7 Brass 0. 1 0. 5 0.7 Aluminum--. 0.0 21. 5 7.8 Radiator Tube- 0. 1 0. 4 0. 2

1 Recommended use dosage.

Corrision Rate with Subject Inhibitor- Recirculating Test (0.5%)

Corrosion Rate, m.p.y. Coupled Insulated Seven day Test:

Cast iron O. 0 0. 0 Copper 0. 1 0. 2 "Bra ss 0. O 0. 0 Aluminum 0. 0 0. 0 Solder 0. 3 Radiator Tube 0.0 Twenty-eight day Test:

ast iron 0. 0 0. 0 Copper 0. 1 0. 2 Brass 0. 1 0. 0 Aluminum 0. 0 0. 0 Solder 0. 0 Radiator Tub 0.0

The corrosion rates which are acceptable for an inhibitor vary according to the use of the metal. Metals which are present in thin sections, at joints or in valves such as radiator tubing, copper, brass or solder, should have corrosion rates of 1 m.p.y. (mils per year) or less. Cast aluminum and cast iron, which are present in thicker sections, can tolerate rates up to 4 m.p.y. or higher, if the corrosion is general. Iron corrosion, however, may also be troublesome from the standpoint of reduced cooling efficiency and blocking of the passageways due to the accumulation of corrosion product. For this reason, the rate for cast iron should be held to a lower value than that which would be dictated by danger of actual penetration.

The above tables clearly demonstrate that the corrosion rates obtained using the subject corrosion inhibitor are very low, in most cases being less than 0.1 m.p.y. It is also apparent that these rates are lower in almost every instance than those obtained using buffered chromate. The highest rate encountered using the subject inhibitor in the recirculation test was 0.3 m.p.y. for solder, which is well below the acceptable amount of 1.0 m.p.y. A comparison of the seven and twenty-eight day recirculating test results indicated that there was no increase in corrosion rates over the longer period. No scaling or fouling of the heat transfer surfaces was noted when the tube from the recirculating test was opened for examination.

The composition of the inhibitor used in Example I was as follows:

Percent Petronate CR (a sodium petroleum sulfonate MW 500-525 8.0 Mercaptobenzothiazole 0.4 n-Butyl alcohol 10.0 Triton X-l14 2.0 Water 7.0 Mineral oil 72.6

EXAMPLE H Inasmuch as the normal operation of a diesel locomotive may result in periods of over or under treatment, it is important that a corrosion inhibitor have a satisfactory safety margin. The corrosion rates of various materials at inhibitor concentrations of 0.25 to 2.0% are set forth in the following table:

Corrosion Results With the Subject Inhibitor at Various Concentrations (Coupled Flask Test Procedure) Concentration, percent 0.25 0.5 1.0 2.0

Corrosion Rate, m.p.y.:

ast iron It is clear from the above that the inhibitor is effective over a Wide range. The highest corrosion rate is 0.5 m.p.y. for copper at a 0.25% concentration. This amount is well below the acceptable rate of 1.0 m.p.y. As has been indicated, the inhibitor is effective down to a concentration percentage of 0.1 to 0.05% or less. Amounts greater than 2.5% can be used but larger quantities make the process economically unattractive.

EXAMPLE III It is preferred in the operation of a diesel cooling system, that zero or low hardness waters be used. In the normal operation of a diesel, however, waters varying in hardness may be encountered. For this reason, it is important that a corrosion inhibitor be capable of functioning satisfactorily in hard as well as soft water. In this test, waters varying in hardness from 30 g.p.g. to deionized water were employed in the flask test procedure. The following table sets forth the results of the test:

Efiect of Hardness on Corrosion Tests Using the As is indicated above, increasing the hardness of the water did not lessen the corrosion inhibiting ability of applicants material. Furthermore, no deposits were encountered in any of the tests.

7 EXAMPLE 1v Another factor that must be considered in selecting a corrosion inhibitor pertains to its ability to withstand the effects of sodium chloride. The amount of sodium chloride found in cooling waters is likely to vary considerably. Tests were made on standard test water which contained 10 g.p.g. of added salt and also on the same water with added salt concentrations of 20 and 40* g.p.g. Although the latter waters are quite corrosive, their action was satisfactorily inhibited by the subject material as is shown in the following table:

Efiect of Sodium Chloride on Corrosion Tests Using the Subject Inhibitor (0.5 %Flask Test Procedure) EXAMPLE V Tests were conducted in order to determine what effect the corrosion inhibitor would have on rubber radiator hose. Rubber radiator hose is the most sensitive nonmetallic material found in a diesel cooling system. Using the flask test procedure, the subject inhibitor was compared with a buffered chromate inhibitor, a commercially available soluble oil, and also with no treatment. After one week, the rubber hose had increased in volume the following amounts:

Rubber Test ResultsFlask Test Procedure Test fluid: Increase in volume percent Chromate treated 6 Subject inhibitor treated 6 Soluble oil treated 34 Untreated 5 It is clear from the above that the subject inhibitor compares favorably with chromate treated cooling systems. Chromate treated waters have caused no field problems in this respect, whereas soluble oil treated water is typical of treatments which have caused serious attack on rubber.

EXAMPLE VI In this experiment the subject corrosion inhibitor was tested in a cooling solution containing 50% standard test Water and 50% ethylene glycol. The results obtained by the flask procedure described in connection with Example I were as follows:

- 50% Standard Test Water Test Medlum {50% Ethylene Glycol Subject Treatment Blank Inhibitor Corrosion Results, m.p.y.:

Coupled Test- 18. 0 0.8 0.3 0. 4 0.3 0.3 0. 2 0. 1 Aluminum 12. 6 0.0

As is evident from the above data, the inhibitor satisfactorily reduced corrosion rates where ethylene glycol was present. Comparable results are obtainable in antifreeze solutions containing methanol, ethanol, glycerine, and other antifreeze agents,

8 EXAMPLE VII It is known that exhaust gases have an adverse effect on certain cooling system treatments, particularly those of the soluble oil type. Investigations have shown that sulfur dioxide is the constituent of the gas which causes the trouble by destroying the emulsion of soluble oil in the cooling system. To determine what effect exhaust gases Would have on the present inhibitor, sulfur dioxide gas was bubbled through water containing the inhibitor at a 0.47% concentration. No change could be detected in the water which indicates that exhaust gases would have no adverse effect on systems containing our inhibitor.

EXAMPLE VIII Although everyone recognizes that it is undesirable to have water in lubricating oils, some water occasionally does leak into a lubricating system. Accordingly, a test was set up to determine Whether our inhibitor would have a harmful effect on the lubricating properties of various oils. In the test, the lubricating ability of various oils containing 1% of the inhibitor was compared with untreated oils. There was no detectable difference between the two materials. The 1% concentration of inhibitor represents approximately the leakage of twice the capacity of a cooling system into a crank case where the inhibitor is maintained at a 0.5% concentration.

In our preferred embodiment, the inhibitor is used at a concentration of about 0.5% based on cooling system capacity. Because of the film-forming properties of the inhibitor, some of the material of the initial application is used for this purpose. Accordingly, it is advisable to add the inhibitor in an amount equivalent to about 1.0%

in the first application to a particular system. Subsequently, the amount can be lowered to 0.5%. Although this is our preferred range, it should be understood that the concentration can be varied considerably and still adequately protect the cooling system.

The particular combination of ingredients disclosed herein produces a unique and superior corrosion inhibitor. Not only does the inhibitor eliminate, or substantially eliminate, corrosion but it also has many other advantages over prior art compounds. The inhibitor is not affected by exhaust gases and it is completely compatible with lubricating oils. The inhibitor is considerably less irritating to the skin and eyes than are the well known chromate additives. The data set forth in the examples show that the inhibitor produces favorable results over wide concentration ranges and that it is not adversely affected by the presence of antifreeze agents.

The unusual properties of the inhibitor result from a combination of a sulfonate, a particular oil, and mercaptobenzothiazole. It is essential that each of these materials be present in the formulation. The sulfonate should have a molecular weight of at least about 425 and preferably from 500 to 525. The mineral oil should be low in aromatics.

It is important to use a dispersing and/or solubilizing agent in the formulation. An ethoxylated nonyl phenol such as Triton Xl 14 is a suitable dispersing agent. In our preferred formulation this material is used at approximately a 25% concentration. Other solubilizers such as n-butyl alcohol can also be employed as needed. It has been found that from 1 to about 15% of n-butyl alcohol is helpful in solubilizing or dispersing the inhibitor when it is first added to the cooling system. Triton X-l l4 aids in maintaining the material in the dispersed state. It would be obvious to those skilled in the art, however, that a great variety of solubilizers or dispersing agents could be used in place of Triton X-1l4 and n-butyl alcohol. For this reason the selection of the particular dispersing or solubilizing agent does not constitute a part of the invention.

The invention is hereby claimed as follows:

1. An aqueous cooling solution for internal combustion engines containing from about 0.1 to about 2.5% of a composition consisting of 2.5 to 25% of an oil-soluble petroleum sulfonate having a molecular Weight of from about 415 to about 525, from about .1 to about 2.0% mercaptobenzothiazole, a dispersing agent, and a mineral oil having an aromatic content of less than about 20%, the ratio of active sulfonate to oil being from about 25:97.5 to about 35:65.

2. An aqueous cooling solution for internal combustion engines containing from about 0.1 to about 2.5% of a composition consisting essentially of 2.5 to 25% of an oil-soluble petroleum sulfonate having a molecular weight of from about 500 to about 525, from about .1 to about 2.0% mercaptobenzothiazole, from to about 15% n-butyl alcohol, from 2 to about 5% of an ethoxylated nonyl phenoyl, and a mineral oil having an aromatic content of less than about 20%, the ratio of active sulfonate to oil being from about 2.5 :97.5 to about 35 :65.

3. An antifreeze cooling solution for internal combustion engines consisting essentially of Water, a material selected from the group consisting of methanol, ethanol, glycerine, propylene glycol, and ethylene glycol, and a composition consisting essentially of from 2.5% to 25 of an oil-oluble petroleum sulfonate having a molecular weight of from about 415 to 525, mercaptobenzothiazole, a dispersing agent, and a mineral oil having an aromatic content of less than about 20%, the ratio of active sulfonate to oil being from about 2.5:97.5 to about 35:65, the proportion of said composition being from about 0.1% to about 2.5%, the amount of said mercaptobenzothiazole being suificient to provide a concentration of at least p.p.m.

4. A method of inhibiting corrosion in the cooling system of an internal combustion engine which comprises adding to said cooling system a corrosion inhibiting amount of a composition consisting essentially of about 2.5 to about 25 of an oil-soluble petroleum sulfonate having a molecular Weight of from about 415 to about 525, mercaptobenzothiazole, a dispersing agent, and a mineral oil having an aromatic content of less than about 20%, said mercaptobenzothiazole being present in said cooling system in an amount suficient to provide a concentration of at least 10 p.p.m., the ratio of active sulfonate to oil being from about 25:97.5 to about 35:65.

5. A method of inhibiting corrosion in the cooling system of an internal combustion engine which comprises adding to said cooling system from about 0.1 to about 2.5% of a composition consisting essentially of from about 2.5 to about 25% of an oil-soluble petroleum sulfonate having a molecular weight of from about 415 to about 525, from about 0.1% to about 2.0% of mercaptobenzothiazole, a dispersing agent, and a mineral oil having an aromatic content of less than about 20%, the ratio of active sulfonate to oil being from about 25:97.5 to about 35:65.

References Cited in the file of this patent UNITED STATES PATENTS Hoover Aug. 21, 1934 FOREIGN PATENTS Great Britain Sept. 11, 1957 OTHER REFERENCES 

1. AN AQUEOUS COOLING SOLUTION FOR INTERNAL COMBUSTION ENGINES CONTAINING FROM ABOUT 0.1 TO ABOUT 2.5% OF A COMBUSTION CONSISTING OF 2.5 TO 25% OF AN OIL-SOLUBLE PETROLEUM SULFONATE HAVING A MOLECULAR WEIGHT OF FROM ABOUT 415 TO ABOUT 525, FROM ABOUT .1 TO ABOUT 2.0% MERCAPTOBENZOTHIAZOLE, A DISPERSING AGENT, AND A MINERAL OIL HAVING AN AROMATIC CONTENT OF LESS THAN ABOUT 20% THE RATIO OF ACTIVE SULFONATE TO OIL BEING FROM ABOUT 35:65. 